For improvement in integration and high performance of a large-scale semiconductor integrated circuit, an increase in density is required, and a reduction in working line width associated with miniaturization of a wiring pattern and realization of multilayered wiring lines are required to cope with the increase in density. Since such a multilayered wiring structure is formed by repeating formation of a conductive film or an insulator film and etching for several times, a difference in height on a surface tends to increase. On the other hand, a focal depth of a resist used for patterning of the wiring lines tends to shallow with miniaturization of the wiring lines, and the difference in height on the surface remarkably affects the patterning, which is seen as a problem. Based on such a background, extensive flattening which can eliminate the difference in height on the surface is required to facilitate the patterning.
As such an extensive flattening technology, there are known a coating technology of a resin such as a polyimide, an etch-back technology for a metal and an insulator film, a reflow technology for a metal and an insulator film, and a chemical mechanism polishing (CMP) technology.
The CMP is a method for pouring slurry containing polishing particles onto a substrate and using a polishing pad attached to a polishing apparatus to perform polishing. At this time, the polishing particles receive a pressure from the polishing apparatus and mechanically polish a surface, and a chemical component contained in the slurry chemically reacts the surface of the substrate so that a surface region of the substrate is thereby chemically removed.
In general, there are various kinds of slurry used for the CMP depending on types or characteristics of a polishing target film. As the polishing particles to be used, there are silica (SiO2), ceria (CeO2), alumina (Al2O3), titania (TiO2), zirconia (ZrO2), and the like, and they can be selectively used in accordance with the polishing target film.
As the CMP slurry which is used for flattening an insulator film such as a silicon oxide film, silica-based slurry is generally examined in conventional examples. The silica-based slurry is manufactured by performing grain growth of silica particles by pyrolysis of a silicon tetrachloride and carrying out pH control with the use of an alkali solution which does not contain an alkali metal such as ammonia.
Further, as the CMP slurry for an inorganic insulator film such as a silicon oxide film, ceria slurry is also used. Since ceria particles have a degree of hardness lower than that of silica particles or alumina particles, a defect such as a scratch is hardly generated on a film surface after the polishing, and hence the ceria particles are considered useful. Furthermore, the ceria particles are known as a strong oxidizing compound and have chemically active properties, and hence the ceria slurry is considered useful for the CMP polishing for an inorganic insulator film such as a silicon oxide film. The ceria slurry used in the CMP polishing is disclosed in Patent Document 1 and Patent Document 2.
In a conventional process of forming an STI (Shallow Trench Isolation), a process in which a silicon nitride film is used as a hard mask is carried out. After the silicon nitride film is formed on a substrate, a trench is formed in a predetermined region of the silicon nitride film and the substrate, a silicon oxide film is formed to fill the trench, and then the silicon oxide film is polished to form an element isolation film. At this time, dry ceria slurry which can assure a high polishing selection ratio of the silicon oxide film and the silicon nitride film is used to polish the silicon oxide film until the silicon nitride film is exposed.
On the other hand, in place of using the silicon nitride film as the hard mask, a polysilicon film is used as a polishing stop film in some situations. In this case, since the polysilicon film has a lower degree of hardness than that of the silicon nitride film, there is a problem that a defect such as a scratch (a scratch defect) is apt to be generated on a polysilicon film surface after the CMP polishing. When a defect, e.g., a scratch is generated on the polysilicon film surface after the CMP polishing, a disconnection failure, a short-circuit failure, or the like is produced in a fine transistor or wiring lines. Wet ceria has a polyhedral structure as compared with the dry ceria, can improve a scratch defect, and is more useful than the dry ceria, but the scratch defect produced in the CMP process has become a more serious problem with further miniaturization of a circuit dimension of a semiconductor device, and a further improvement is demanded.
Thus, as a method for reducing scratch defects, Patent Document 3 discloses a method for improving the scratch defects by using fine tetravalent metal hydroxide particles as abrasive grains. However, according to such a method, although the scratch defects can be improved by reducing a size of the abrasive grains, there arises a problem of a reduction in polishing speed.
Further, when a circuit dimension of a semiconductor device is further miniaturized, besides the scratch defects, a problem of insufficiency of a polishing section ratio arises. When the CMP polishing is performed with the use of a polishing agent having a low polishing selection ratio of a silicon oxide film and a polysilicon film, there occurs a problem that the polysilicon film as a polishing stop film is excessively polished, and an improvement is demanded.
For example, Patent Document 4 discloses slurry containing a polyoxyethyleneamine ether as a polysilicon polish finishing agent, and Patent Document 5 discloses slurry containing at least one type of saccharide selected from a group consisting of cationized polyvinyl alcohol, amino sugar or a derivative thereof, a polysaccharide having an amino sugar, and a derivative thereof. However, these types of slurry do not have a sufficient polysilicon film protecting function, and a problem of cleaning performance after the CMP polishing arises, and improvement is required.